Chapter 3: Reproduction of Organisms

Reproduction and Genetics

Code of Life This is a computer- generated model of DNA, the material that carries genetic information. This type of image helps to accu- rately display the chemistry of mole- cules in the body.

10,000–9,000 Years Ago 1870–1890 People in Mexico and south- Luther Burbank works in Santa Rosa, ward plant food crops using California, developing more than 800 seeds and shoots from parent new strains of plants to improve the plants. quality of food; he is known as the father of plant breeding.

A.D. 1 1700 1800 1900

2,700 Years Ago 1791 1890s Greeks develop differ- James Weatherby pub- The invention of bet- ent varieties of plants lishes book of pedigrees ter microscopes by grafting (splicing of race horses in England, allows several scien- part of one plant with which becomes basis for tists to discover the part of another). recording pedigrees of basic facts of sexual other animals. reproduction.

120 (bkgd)Will & Deni McIntyre/Photo Researchers, Luther Burbank Home & Gardens/Santa Rosa, California To learn more about biologists and their work, visit ca7.msscience.com .

Interactive Time Line To learn more about these events and others, visit ca7.msscience.com .

1997 2001 2005 The U.S. Department of Scientists in Washing- Scientists at UC Davis Energy sets up Joint ton identify a mutation work on a bank of Genome Institute (JGI) that causes harmful dog pedigrees based to study DNA; JGI is drug responses in dogs. on DNA. operated by the Univer- sity of California. 1950 1960 1970 1980 1990 2000 2010

1951, 1952, 1953 1997 February 2001 Rosalind Franklin has a photo- Scientists in Scotland Scientists from around graph of DNA; Martha Chase announce the cloning the world successfully and Alfred Hershey prove that of a sheep named Dolly. map the human genome DNA is the molecule of heredity; (all the genes of the Francis Crick and James Watson human body). model DNA.

121 (t)Henry T. Kaiser/PictureQuest, (b)Roslin Institute Reproduction of Organisms

/ iÊ Ê`i> Different types of reproduction ensure the survival of different species.

LESSON 1 2.b, 7.b Sexual Reproduction and > Meiosis } `i> *VÌÕÀi >Ê`i> Meiosis maintains the chromosome number,i>` of} a species from oneiV generation to the next.

LESSON 2 2.a, 5.f, 7.b > } Plant`i> Reproduction*VÌÕÀi >Ê`i> A plant’s life ,i>`} cycle includes iV a diploid generation that produces spores and a haploid generation that produces eggs and sperm.

LE SSON> 3 } 2.a, 2.b, 7.c Animal`i> Reproduction*VÌÕÀi ,i>`} >Ê`i> iV Animals have specialized structures for sexual reproduction.

LESSON 4 2.a, 7.a, 7.c, 7.d, 7.e Whhoo pplantedlanted aallll ooff tthesehese fflowers?lowers? > } Asexualì> Reproduction*VÌÕÀi Some of these yellow poppies and purple lupines might have grown from seeds produced in flowers that bloomed here the previous year. Or, an >Êì>,i>`} Asexual iV animal passing by might have deposited some seeds in its wastes. Still reproduction produces other plants might have grown from parts of existing plant roots or stems. offspring that are identical to the parent. -ViVi-ViViÊÊÊÊ+PVSOBM List four plants you familiar with that grow from seeds. List other ways you know of that plants can be grown. 122 > } ì> *VÌÕÀi

,i>`} iV Start-Up Activities

Plant Reproduction Make the following Foldable How does reproduction about sexual and asexual happen? reproduction in flowering plants. When a photograph is reproduced, a copy is made. Does the same thing happen when an STEP 1 Fold a sheet of paper in half organism reproduces? lengthwise. Fold the top down about 3 cm from the top. Procedure 1. Create a spider concept map about what you know about reproduction. 2. Write the word reproduction in the center circle and add examples of reproduction around it. Think About This • Infer Art and photographs can be reproduced. Does the same thing happen when an organism reproduces? STEP 2 Unfold and draw lines along the folds as shown. Label the top and each • Compare List ways that puppies are like column. their parents and ways they could be different from their parents. N 'LOWERINGPLANT • Predict Do plants have parents? Do REPRODUUCTION bacteria have parents? 4EXUAL "SEXUAL • Analyze Some organisms look like their parents, but others do not. How might this happen? 2.a, 7.d

Clarifying As you read Lesson 2, list in the appropriate column the flowering-plant structures involved in each type of reproduction. Visit ca7.msscience.com to:

▶ view ▶ explore Virtual Labs ▶ access content-related Web links ▶ take the Standards Check

123 GGetet RReadyeady ttoo RReadead New Vocabulary

Learn It! What should you do if you find a word you don’t know or understand? Here are some suggested strategies:

1. Use context clues (from the sentence or the paragraph) to help you defi ne it. 2. Look for prefi xes, suffi xes, or root words that you already know. 3. Write it down and ask for help with the meaning. 4. Guess at its meaning. 5. Look it up in the glossary or a dictionary.

Practice It! Look at the word conifer in the following passage. See how context clues can help you understand its meaning.

Context Clue The most common gymnosperms are conifers. Examples of conifers are pines, Conifers, such as pines, firs, cypresses, red- firs, cypresses, redwoods, and yews, are trees and shrubs with woods, and yews. needlelike or scalelike leaves. Most conifers are evergreen and can live for many years. Bristlecone pines, shown in Figure 11, are among the Context Clue oldest living trees on Earth. —from page 137 Conifers are trees and shrubs with needlelike or scalelike leaves.

Context Clue Most conifers are evergreen and can live for many years. Apply It! Make a vocabulary bookmark with a strip of paper. As you read, keep track of words you do not know or want to learn more about.

124 aph contain- Read a paragr a vocabulary word from ing end. Then, go Target Your Reading beginning to Use this to focus on the main ideas as you read the chapter. back to determinethe wo therd. ning of 1 Before you read the chapter, respond to the statements mea below on your worksheet or on a numbered sheet of paper. • Write an A if you agree with the statement. • Write a D if you disagree with the statement. 2 After you read the chapter, look back to this page to see if you’ve changed your mind about any of the statements. • If any of your answers changed, explain why. • Change any false statements into true statements. • Use your revised statements as a study guide.

Before You Read Statement After You Read A or D A or D 1 All living organisms have two parents.

2 Parents always pass their genetic material to their offspring.

3 Not all reproduction involves a sperm cell and an egg cell.

4 Meiosis is a type of cell division.

5 All plants reproduce by forming flowers.

6 All plants reproduce by forming seeds.

Print a worksheet of 7 Some animal embryos develop inside the body of the this page at mother. ca7.msscience.com . 8 All animal embryos develop inside eggs.

9 Some organisms have only one parent.

10 Plants can be cloned, but animals cannot.

125 LESSON 1

Science Content Standards Sexual Reproduction 2.b Students know that sexual reproduction produces offspring that inherit and Meiosis half their genes from each parent. >Ê`i> Meiosis maintains the chromosome number of a 7.d Construct scale models, maps, and species from one generation to the next. appropriately labeled diagrams to communicate scientific knowledge (e.g., Real-World Reading Connection You have a better chance motion of Earth’s plates and cell structure). of seeing a wild California condor than your parents did when they were your age. In the 1980s, fewer than 20 of these birds were in the wild. Naturalists captured condors and helped them Reading Guide produce offspring. Some of these condor offspring now live in > } the wild, and*VÌ ÕtheÀi condor population is increasing. What You’ll Learn `i> ,i>`} ▼ Compare a sexually What iV is sexual reproduction? produced offspring to its parents. Many young organisms resemble their parents, such as the guinea pig pups shown in Figure 1. Like most animals, each

▼ Explain the importance guinea pig pup has two parents—a mother and a father. The of meiosis in sexual reproduction. genetic material that an organism receives from its parents determines what it looks like and how it functions.

▼ Sequence meiosis. Reproduction in organisms produces new offspring. Sexual

▼ Describe the results of reproduction is the production of an offspring that results meiosis. when the genetic materials from two different cells combine. Half of the genetic material is contained in an egg cell. The Why It’s Important other half is contained in a sperm cell. A process called If you know how cells divide fertilization (fur tuh luh ZAY shun) is the fusing together of a for reproduction, it’s easier to understand why offspring sperm cell and an egg cell. The new cell that forms is called a resemble their parents. zygote (ZI goht). A zygote develops into a new organism.

Vocabulary Figure 1 These guinea pig pups are not identical sexual reproduction because each one inherited a different mix of genetic egg material from its parents. sperm fertilization zygote meiosis diploid haploid Review Vocabulary eukaryote: an organism made of cells; each cell has a membrane-bound nucleus (p. 64)

126 Chapter 3 • Reproduction of Organisms Advantages of Sexual Reproduction Sexual reproduction is the most common form Figure 2 Each California poppy plant in this population has a unique set of genetic of reproduction in eukaryotes. As you just read, information, making the population geneti- offspring from sexual reproduction receive cally varied. genetic material from two cells. Each guinea pig pup in Figure 1 inherited genetic material from the same two parents. Each pup inherited a different mix of genetic material. In a population of guinea pigs, or any other species that reproduces sexually, no two individuals, except identical twins, have the same mix of genetic material. This means that each individual has a different set of traits. The variety of genetic traits in a population of the same species is known as genetic variation. How does genetic variation affect the survival of a species?

Genetic Variation When environmental conditions change, genetic variation can help a species survive. Imagine a population of California poppies, like those shown in Figure 2. During a drought, poppy plants with traits that enable them to grow in dry conditions are more likely to survive and produce seeds. Plants without these traits might not survive. Because their genetic makeups vary, the population of poppies would ACADEMIC VOCABULARY include a few plants that could survive a drought. vary (VAYR ee) A lack of genetic variation can cause problems (verb) to make different for a species. Suppose every plant in the poppy Musicians vary the tempo as directed by the conductor. population had the same genetic traits. If none of those traits enabled the plants to survive hot, dry weather, the entire population might die out.

Selective Breeding Plant breeders and animal Figure 3 The golden retriever is one of breeders often select a male organism and a many dog breeds created by mating dogs female organism with certain preferred traits to that have similar genetic material. be the parents of offspring. This method of sexual reproduction is called selective breeding. It produces groups of organisms with similar traits, such as the dogs shown in Figure 3, but reduces genetic variation. Offspring produced by selective breeding can also inherit health problems. Figure 3 Why do these puppies resemble each other more than the guinea pig pups resemble each other?

Lesson 1 • Sexual Reproduction and Meiosis 127 Figure 4 Male sea urchins release sperm into the water at the same time that female sea urchins release millions of eggs. Male elephant seals might attack each other to become the dominant male that mates with female elephant seals.

Disadvantages of Sexual Reproduction Because males produce sperm and females produce eggs, one of the disadvantages of sexual reproduction is getting egg and sperm together for fertilization. Some species, such as the sea urchin SCIENCE USE V. COMMON USE shown in Figure 4, produce millions of egg cells or sperm cells and reproduce Science Use to produce living release them into water. This increases the chances that a sperm offspring. Some plants can will find an egg. Other organisms have specific methods that reproduce with only one ensure fertilization. parent plant. Another disadvantage of sexual reproduction is the time needed Common Use to copy. The hardware store has a machine for organisms to grow and develop until they can reproduce. For that can reproduce keys. example, male elephant seals, as shown in Figure 4, do not mate until they are about 9–10 years of age. Humans are even older. Later in this chapter, you will read about types of reproduction that can happen before organisms grow and develop enough to reproduce sexually and do not require fertilization. Why is meiosis important? You read in Chapter 1 that genetic material is part of the chromosomes in the nucleus of each eukaryotic cell. Sexual reproduction includes fertilization, which is the combining of the genetic WORD ORIGIN material in a sperm cell and the genetic material in an egg cell. meiosis Meiosis (mi OH sus) is cell division that produces sperm or eggs from Latin meioun; means to from certain reproductive cells in an organism. Meiosis takes place lessen only in eukaryotes that reproduce sexually.

What kinds of cells does meiosis produce?

Meiosis is important because it ensures that a species’ offspring inherit the correct chromosome number. For example, tomatoes inherit 24 chromosomes, humans inherit 46 chromosomes, and chickens inherit 78 chromosomes. Without meiosis, the chromosome number would double with each generation. Instead of inheriting 46 chromosomes, children would inherit 92 chromosomes, their children would inherit 184, and so on.

128 Chapter 3 • Reproduction of Organisms Maintaining Diploid Cells Recall from Chapter 2 that homologous (huh MAH luh gus) chromosomes are similar in size, shape, and genetic material. A diploid cell in an organism contains pairs of chromosomes that equal the chromosome number of that organism’s species. A diploid human cell has 23 pairs of homologous chromosomes. The chromosome number for humans is 46. Homologous chromosomes are similar, but not identical. For example, each human chromosome in a homologous pair might contain genetic material for eye color. However, one chromosome might have blue eye-color information and the other brown eye- color information. Creating Haploid Cells Sperm and egg cells have half the chromosome number of the species. For example, a human sperm cell contains 23 chromosomes—one chromosome from each homologous pair of chromosomes. Similarly, a human egg cell contains 23 chromosomes. A cell that contains one chromosome from each homologous pair is WORD ORIGIN called a haploid cell. haploid It’s important for offspring to inherit the correct number of from Greek haploeides; means chromosomes for their species. Because an egg and a sperm are single haploid, the chromosome number of offspring does not double, as described on the previous page. Meiosis ensures that fertilization creates a zygote with the correct number of chromosomes, as shown in Figure 5.

Figure 5 Meiosis ensures that the chromosome number of a species stays the same from one generation of offspring to the next. Interpret How is a diploid cell created?

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Lesson 1 • Sexual Reproduction and Meiosis 129 What are the phases of meiosis? In Chapter 2, you read about the stages of mitosis—the division of a cell nucleus. Meiosis happens in a similar way. For example, before meiosis begins, a cell’s chromosomes replicate, just as they do before mitosis. Recall that each replicated chromosome consists of two identical sister chromatids that are held together near their middles. In mitosis, division of the nucleus and cytokinesis happen once. In meiosis, division of the nucleus and cytokinesis happen twice. These two processes are called meiosis I and meiosis II. Like mitosis, the phases of each process are called prophase, metaphase, anaphase, and telophase. Diagrams of the phases of meiosis I and meiosis II are shown in Figure 6. Phases of Meiosis I Prophase I The membrane surrounding the nucleus breaks apart. The replicated chromosomes condense and thicken. Then, unlike mitosis, homologous chromosomes line up close to each other.

Metaphase I The pairs of replicated homologous chromosomes form a line along the middle of the cell. Fibers of the cytoskeleton attach to each pair of sister chromatids.

Anaphase I Cytoskeleton fibers pull each pair of sister chromatids to opposite ends of the cell. Notice that the pairs of replicated homologous chromosomes separate, but not the sister chromatids. Sister chromatids stay together.

Telophase I A membrane forms around each group of replicated chromosomes. Then, the cytoplasm divides to form two daughter cells. Sister chromatids still are together. Phases of Meiosis II During meiosis II, the nucleus of each daughter cell formed during meiosis I divides. Then, each daughter cell divides.

Prophase II Chromosomes do not replicate before prophase II. They remain condensed and thickened.

Metaphase II The cytoskeleton fibers move the replicated chromosomes to the middle of the cell.

Anaphase II The sister chromatids of each replicated chromosome separate and move toward opposite ends of the cell.

Telophase II A membrane forms around each set of chromatids, which now are called chromosomes. The cytoplasm divides, and meiosis II is complete.

130 Chapter 3 • Reproduction of Organisms Figure 6 Meiosis produces four haploid daughter cells from one diploid parent cell. Meiosis I separates homologous chromosome pairs. Meiosis II separates sister chromatids. Identify other differences between meiosis I and meiosis II.

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Telophase I—Nuclear membrane forms around each set of sister chromatids and the cytoplasm divides, forming two daughter cells.

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Prophase II—Nuclear membrane breaks apart.

Metaphase II—Chromosomes line up along the center of the cell.

Anaphase II—Sister chromatids of each chromosome begin to separate and move to opposite ends of the cells.

Telophase II—A nuclear membrane forms around each set of chromatids, and the cytoplasm divides.

JcYjea^XViZY To see an animation of meiosis, X]gdbdhdbZh visit ca7.msscience.com. What are the results What does of meiosis? meiosis look As you read earlier, meiosis is similar to mitosis, but there are like? important differences. Some of the similarities and differences are listed in Table 1. How do chromosomes move during meiosis? Try Both meiosis and mitosis begin with one diploid parent cell. this lab to model meiosis. Both meiosis and mitosis take place only in eukaryotic cells. Recall that eukaryotic cells are cells that contain a nucleus surrounded by a membrane. In meiosis, the nucleus of the parent cell divides, then the two newly formed nuclei divide. Mitosis has only one division of a Procedure nucleus. Also, mitosis is usually followed by cytokinesis that results in two daughter cells of equal size. Sometimes when meiosis 1. Complete a lab safety occurs for egg production, the cytoplasm divides unequally during form. meiosis I. This results in a small cell that breaks down and a large 2. Use Figure 6 for refer- cell that undergoes meiosis II. In meiosis II, the cytoplasm divides ence as you model unequally again. The larger cell becomes the egg and the smaller meiosis. cell breaks down. 3. Model each phase of meiosis I and meio- Table 1 What process produces genetically different sis II using colored daughter cells? yarn to represent chromosomes. Table 1 Comparison of Meiosis and Mitosis 4. Use scissors to cut the lengths of yarn to Characteristic Meiosis Mitosis create homologous chromosomes. Number of diploid diploid 5. Glue your yarn chromosomes in chromosomes to parent cell construction paper circles provided by Type of parent cell only certain nearly all your teacher. reproductive cells in eukaryotic cells eukaryotic organisms Analysis 1. Explain how your Number of divisions of 21 understanding of meio- nucleus sis improved after you completed this lab. Number of daughter 42 cells produced 2. Evaluate Is yarn a good material to use Chromosome number haploid diploid for modeling chromo- in daughter cells somes during meiosis? Functions in the • produces sperm • daughter cells 3. Describe ways in which organism and egg cells genetically this model worked • maintains identical to each well. List ways you chromosome other and to the could improve it. number for the parent cell species • growth, cell repair, 2.b, 7.d some types of reproduction

132 Chapter 3 • Reproduction of Organisms Meiosis Summary In this lesson, you learned that sexual reproduction includes fertilization—the fusion of a sperm cell with an egg cell. You also learned that fertilization produces a cell called a zygote. The zygote is a diploid cell, and an egg and a sperm are called haploid cells. Sperm and egg cells are produced by meiosis. It is important to remember that all the eggs or sperm produced by an organism are different. Therefore, each zygote produced by sexual reproduction from the same parents will inherit different genetic material. This genetic variation can be important to the survival of a species. You will learn more about how meiosis promotes genetic diversity when you study genetics in Chapter 4.

LESSON 1 Review

Summarize Standards Check Create your own lesson Using Vocabulary 6. Give an example of how summary as you organize sexual reproduction increases 1. Distinguish haploid from an outline. genetic diversity. 2.b diploid. 2.b 1. Scan the lesson. Find and 7. Simplify meiosis into its list the first red main 2. In your own words, write the basic events. 2.b heading. definition for meiosis. 2.b Applying Science 2. Review the text after Understanding Main Ideas the heading and list 2–3 8. Analyze why meiosis is not details about the heading. 3. Why is meiosis important in the type of cell division that 3. Find and list each blue sexual reproduction? produces new skin cells. 2.b subheading that follows A. It produces haploid daugh- 9. Suggest why brothers who the red main heading. ter cells. 2.b have the same parents are 4. List 2–3 details, key terms, B. It produces diploid daugh- not identical. 2.b and definitions under ter cells. each blue subheading. C. It replicates chromosomes. 10. Organize Information Copy the graphic organizer below 5. Review additional red D. It produces four daughter and fill it in with details about main headings and their cells. meiosis I and meiosis II. 2.b supporting blue subhead- 4. How many chromosomes are ings. List 2–3 details about in a sperm cell compared to a each. Meiosis I skin cell? ELA7: W 2.5 A. same number 2.b Meiosis II B. half as many C. three times as many D. twice as many Science nline 5. List the phases of meiosis in the order they occur. 2.b For more practice, visit Standards Check at ca7.msscience.com .

Lesson 1 • Sexual Reproduction and Meiosis 133 LESSON 2

Science Content Plant Reproduction Standards 2.a Students know the differences >Ê`i> A plant’s life cycle includes a diploid generation between the life cycles and reproduction that produces spores and a haploid generation that produces methods of sexual and asexual organisms. eggs and sperm. 5.f Students know the structures and Real-World Reading Connection In early spring, you might processes by which flowering plants see cars or sidewalks covered with something that looks like yel- generate pollen, ovules, seeds, and fruit. 7.d Construct scale models, maps, and low dust. Where did it come from? It came from some plants that are reproducing. As in all living things, reproduction is part appropriately labeled diagrams to > } communicate scientific knowledge (e.g., of` thei> life *cyclesVÌÕÀi of plants. motion of Earth’s plates and cell structure). ,i>`} What iV is alternation of generations? Reading Guide The human body is made primarily of diploid cells. The only human haploid cells are sperm or eggs. As a result, you will live What You’ll Learn your entire life as a diploid organism. To put it another way, your

▼ Explain alternation of life cycle includes only a diploid stage. generations. That isn’t true for all organisms. Some organisms, including

▼ Summarize reproduction plants, have two life stages called generations. One generation in seedless plants. has primarily diploid cells. The other generation has only

▼ Distinguish between haploid cells. Organisms that alternate between diploid and reproduction in flowerless haploid generations have an alternation of generations as shown and flowering plants. in Figure 7.

▼ Identify the reproductive structures in a flower and Figure 7 Why does the haploid generation begin state their functions. with meiosis? Why It’s Important Learning how plants repro- Figure 7 The life cycles of all plants include an alternation duce helps you understand of generations. The diploid generation begins with fertiliza- important differences tion. The haploid generation begins with meiosis. between plants and animals. 9êad^Yon\diZ 9êad^YeaVci Vocabulary spore filament pollen grain pistil ovule stigma seed style ;ZgiâôVi^dc angiosperm ovary BZ^dh^h stamen pollen tube anther fruit Review Vocabulary HeZgb :\\ mitosis: a process in which the nucleus of the cell =Vead^YhedgZh divides (p. 91) =Vead^YeaVci 134 Chapter 3 The Diploid Generation When you look at a tree or a flower, you’re seeing part of the diploid generation of a plant. Meiosis occurs in certain cells in the reproductive structures of a diploid plant. The daughter cells produced from haploid structures are called spores. Spores grow by mitosis and cell division to form the haploid generation of a plant. The Haploid Generation In most plants, the haploid generation is tiny and lives sur- ACADEMIC VOCABULARY rounded by specific tissues of the diploid plant. In other plants, specific (spih SIHF ihk) the haploid generation lives on its own. Certain reproductive cells (adj) relating to or being an of the haploid generation produce haploid sperm and/or eggs by example of a certain kind of thing mitosis and cell division. Fertilization takes place when a sperm The race car needs a specific and an egg fuse to form a diploid zygote. Through mitosis and cell type of fuel. division, the zygote grows into the diploid generation of the plant. How are the sperm and eggs produced by the haploid generation of a plant formed? How do seedless plants reproduce? You’ve probably planted seeds and watched them grow into new plants. But, not all plants grow from seeds. The first land plants to inhabit Earth probably were seedless plants—plants that grow from haploid spores, not from seeds. The mosses and ferns in Figure 8 are examples of seedless plants found on Earth today. The life cycle of a moss is typical for some seedless plants. It begins with haploid spores that grow by mitosis and cell division into haploid plants. The tiny, green moss plants that carpet rocks, bark, and soil in moist areas are haploid plants. They have male structures that produce sperm and female structures that produce eggs. Fertilization results in a diploid zygote that grows by mitosis and cell division into the diploid generation. The diploid generation of mosses is tiny and not easily seen. It produces haploid spores by meiosis, and the cycle repeats.

Figure 8 Mosses and ferns usually grow in moist environments. Sperm must swim through a film of water to reach an egg.

Diploid Moss Generation

Lesson 2 • Plant Reproduction 135 How do seed plants reproduce? Figure 9 Pollen grains of one type of Most of the land plants that cover Earth grew from seeds. Plants plant are different that grow from seeds are called seed plants. There are two groups from those of any of seed plants—flowerless seed plants and flowering seed plants. other type of plant. Unlike seedless plants, the haploid generation of a seed plant is Infer how scientists might use this characteristic of within diploid tissue. Separate diploid male and diploid female pollen grains. reproductive structures produce haploid sperm and haploid eggs that join during fertilization. The Role of Pollen Grains A pollen (PAH lun) grain forms from tissue in a male reproductive structure of a seed plant. Each pollen grain contains nutrients and has a hard, protective outer covering, as shown in Figure 9. Sperm cells form inside pollen grains. Wind, animals, gravity, or water currents can carry pollen grains to female reproductive structures. Plants cannot move to find a mate like most animals can. Recall reading about the yellow dust at the beginning of this chapter. That dust was pollen grains. Male reproductive structures produce a vast number of pollen grains. When pollen grains land on a female reproductive structure of a plant that is the same species as the pollen grains, pollination (pah luh NAY shun) occurs. The Role of Ovules and Seeds The female reproductive structure of a seed plant contains one or more ovules. A haploid egg develops inside each ovule. Follow- ing pollination, sperm enter the ovule and fertilization occurs. A seed, as shown in Figure 10, develops from an ovule after fertilization. It consists of an embryo, a food supply, and a protective covering. The embryo (EM bree oh) is an immature diploid plant that developed from the zygote. A seed’s food supply provides the embryo with nourishment for its early growth.

Figure 10 A seed contains a diploid plant embryo and a food supply protected by a hard outer covering.

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136 Chapter 3 • Reproduction of Organisms Female cones

Male cones

Female cone

Western Bristlecone Pine Inyo National Forest, CA

Macnab Cypress Colusa County, CA

Figure 11 Pollen-producing male cones usually are smaller than female cones. Seeds form at the base of each scale on a female cone. To see an animation of gymnosperm reproduction, visit ca7.msscience.com. How do flowerless seed plants reproduce? Flowerless seed plants are also known as gymnosperms (JIHM nuh spurmz). The word gymnosperm means “naked seed” and gymnosperm seeds are not surrounded by a fruit. The most common gymnosperms are conifers. Conifers, such as pines, firs, cypresses, redwoods, and yews, are trees and shrubs with needlelike or scalelike leaves. Most conifers are evergreen and can live for many years. Bristlecone pines, such as the one shown in Figure 11, are among the oldest living trees on Earth. Cones are the male and female reproductive structures of conifers. They contain the haploid generation. Male cones are papery and produce pollen grains. Female cones are woody, berry- like, or soft and produce eggs. Seeds form as part of the female cone.

Lesson 2 • Plant Reproduction 137 !"#$% & " How do flowering seed plants reproduce? What’s in a Do you enjoy the fragrance of roses or the bold colors of lilies? flower? These are examples of flowering seed plants, also known as Sexual reproduction in angiosperms (AN jee uh spurmz). Most of the plants you see flowering plants involves around you are angiosperms. Fruits and vegetables come from male and female parts of flowers. Can you discover angiosperms. Many animals depend on angiosperms for food. which parts are which? Reproduction and the Flower Procedure Reproduction of an angiosperm begins in a flower. A typical flower has male and female reproductive organs surrounded by 1. Complete a lab safety petals, as shown in Figure 12. Most flowers have several male form. reproductive organs but only one female reproductive organ. Some 2. Obtain a flower from flowers have only male or only female organs. your teacher. The male reproductive organ of a flower is the stamen. Pollen 3. Examine it with a part- ner. Make a sketch. grains form at the tip of the stamen, in a structure called the Label your sketch anther. The filament is a long stalk that supports the anther and according to Figure 12. connects it to the base of the flower. 4. Using a scalpel, care- The female reproductive organ of a flower is the pistil. At the fully cut the flower in tip of the pistil is the stigma, where pollen can land. The stigma is half lengthwise. at the top of a long tube called the style. At the base of the style is the ovary. Inside the ovary is usually one or more ovules. As you read earlier in this lesson, each ovule eventually will contain a haploid egg.

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To see an animation of the angiosperm Figure 13 In the life life cycle, visit ca7.msscience.com . cycle of a flowering plant, the haploid generation grows and What is an angiosperm’s life cycle? develops inside the diploid plant. A typical life cycle for an angiosperm is shown in Figure 13. Pollen grains travel by wind, gravity, water, or an animal from the anther to the stigma, where pollination occurs. A pollen tube grows from the pollen grain into the stigma, down the style, to the ovary at the base of the pistil. Sperm develop from a haploid cell in the pollen tube. When the pollen tube enters an ovule, the sperm are released and fertilization takes place. WORD ORIGIN angiosperm Do sperm develop before or after pollination? angio- from Greek angeion, means a vessel; and As you read earlier, the zygote that results from fertilization -sperm from Greek sperma, means seed develops into an embryo. Each ovule and its embryo will become a seed. The ovary, and sometimes other parts of the flower, will develop into a fruit that contains one or more seeds. The seeds can grow into new, genetically related plants that produce flowers, and the cycle repeats.

Lesson 2 • Plant Reproduction 139 Table 2 Flowers, Fruits, and Seeds of Common Plants Plant Flower Fruit Seed Pea

Corn

Strawberry

Dandelion

Interactive Table To organize information about flowers, fruits, and seeds, visit ca7.msscience.com .

Table 2 Which of the fruits has seeds on the outside?

Fruit and Seed Dispersal Fruits and seeds, including the peas, corn, and strawberries shown in Table 2, are important sources of food for people and animals. In most cases, seeds of flowering plants are contained inside fruits. Green pods are the fruits of a pea plant. The peas nestled inside a peapod are the seeds. A cob is the fruit of a corn plant. The kernels on a cob are the seeds. Strawberries have tiny seeds on the outside of the fruit. We usually think of fruits as juicy and edible, like an orange or a watermelon. However, some fruits are hard and dry, and not particularly edible. Each parachutelike structure of a dandelion is a dry fruit. Fruits help protect seeds and help scatter or disperse them. For example, some fruits, like that of a dandelion, are light enough to float on air currents. When an animal eats a fruit, the fruit’s seeds can pass through the animal’s digestive system with little or no damage. Imagine what happens when an animal, such as the mouse shown in Figure 14, eats blackberries. The animal digests the juicy fruit, but deposits the seeds on the soil with its wastes. By the time that this happens, the animal might have traveled some distance away from the blackberry bush. This means that the animal helped to disperse the seed away from the blackberry bush.

140 Chapter 3 • Reproduction of Organisms ! # $ % &'& ( ' ( ( ) $ ( ' ( $ * +!( * %, +!( Visualizing Seed Dispersal

Figure 14 Wind, water, gravity, and animals help disperse plant seeds.

▲ Some seeds are inside of dry fruits that have tiny hooks. These hooks can attach to fur, feathers, or clothing and as a ▲ Some animals, such as this result, the seeds inside the fruit move to new locations. squirrel, bury or hide fruits and seeds far from the parent plant. ▲ Pressure If not found and eaten, the seed builds within can sprout. the seedpods of a jewelweed plant until the pod explodes. This propels the seeds far from the parent plant.

▲ A coconut is a type of seed that can float. Floating ▲ The seeds of fruits seeds are often usually are not damaged carried many when they pass through an kilometers from animal’s digestive tract. When the parent the animal excretes the seeds plant. with its wastes, the seeds are usually moved to a location far from the parent plant.

Contributed by National Geographic Lesson 2 • Plant Reproduction 141 % Plant Reproduction Summary In this lesson, you learned that plants reproduce sexually. All plant life cycles include an alternation of generations—they alternate between a haploid generation and a diploid generation. Most of the plants you see around you, including trees, flowers, and grasses, are the diploid generation. Familiar mosses are haploid plants that grew from a haploid spore. The diploid stage is small and often overlooked. Ferns are diploid plants. The haploid stage is small and rarely seen. Conifers and flowering plants are diploid seed plants. The haploid stage of seed plants is surrounded by diploid tissue. Seed plants reproduce by forming seeds. In conifers, seeds form as part of a female cone. In flowering plants, seeds form as part of a flower.

LESSON 2 Review

Summarize Standards Check Create your own lesson Using Vocabulary 6. Compare the life cycles of summary as you write a flowerless seed plants and Complete the sentences using the newsletter. flowering seed plants. 2.a correct term. 1. Write this lesson title, Applying Science number, and page num- fruit anther spores bers at the top of a sheet 1. The diploid generation of 7. Assess What criteria would of paper. a plant produces haploid you use to assess the repro- 2. Review the text after that grow to be- ductive success of a plant? 2.a the red main headings come the haploid generation. 8. Organize Information Draw and write one sentence 5.f a graphic organizer similar to about each. These will be 2. The flower part in which pol- the one below to list the the headlines of your female parts of a flower. Write newsletter. len grains form is the . 5.f “female flower parts” in the 3. Review the text and write center oval. 5.f 2–3 sentences about each 3. Angiosperm seeds are part of blue subheading. These a(n) . 5.f sentences should tell who, what, when, where, and Understanding Main Ideas why information about each headline. 4. Which is NOT used to define alternation of generations? 4. Illustrate your newsletter with diagrams of impor- A. chromosome 2.a tant structures and pro- B. diploid cesses next to each C. haploid headline. D. spore ELA7: W 2.5 5. State the functions of a repro- Science nline ductive structure flower. 5.f For more practice, visit Standards Check at ca7.msscience.com.

142 Chapter 3 • Reproduction of Organisms Seed Plants ca7.msscience.com

LESSON 3

Science Content Animal Reproduction Standards 2.a Students know the differences >Ê`i> Animals have specialized structures for sexual between the life cycles and reproduction reproduction. methods of sexual and asexual organisms. Real-World Reading Connection Have you ever found a 2.b Students know that sexual reproduction cluster of tiny, beadlike things on the underside of a leaf? What produces offspring that inherit half their genes from each parent. could they be? They might be eggs laid by a butterfly, a ladybug, 7.c Communicate the logical connection or some other insect. Eggs are an important part of the life cycle among hypotheses, science concepts, tests of all animals. > } conducted, data collected, and conclusions `i> *VÌÕÀi drawn from the scientific evidence. What,i>` }are animal reproductive organs iV called? Reading Guide Animals often have external physical characteristics that dis- What You’ll Learn tinguish males from females. For example, it’s fairly easy to tell the difference between the male and female animals shown in

▼ Explain the role of male Figure 15. In mammals and birds, males are often larger or and female reproductive organs. more colorful than females.

▼ Differentiate between internal and external fertilization.

▼ Compare and contrast embryo development in animals. Why It’s Important Learning how animals reproduce will help you understand human Lions reproduction.

Vocabulary Figure 15 Male and gonad female animals often have testes different physical charac- ovary teristics. A lion has a ruff metamorphosis of fur around his neck and is larger than the lioness. Review Vocabulary A peacock has larger and organ: structure of an more colorful tail feathers organism made of different than a peahen. types of tissues that work Compare Which of these together (p. 104) animals are male and which are female? How do you know? Peacocks

Lesson 3 • Animal Reproduction 143 BVaZ ;ZbVaZ DkVgn IZhi^h

Figure 16 Sperm cells are produced by meiosis in the testes of male animals. Meiosis in one or two ovaries of female animals produces egg cells.

Male Reproductive Organs The reproductive systems of animals include specialized reproductive organs called gonads that produce sperm or eggs. Figure 16 shows the reproductive systems of male and female ACADEMIC VOCABULARY chickens. Male animals have gonads called testes that produce network (NET wurk) sperm. Testes contain a network of coiled tubes in which sperm (noun) a system of lines or cells form. Sperm have tails that enable them to swim through channels that connect with fluid to reach an egg cell. Most male animals have two testes each other. The capillaries, veins, and arteries form a located inside the body cavity. network for moving blood. What type of cell forms in the testes?

Vertebrate animals—animals with backbones—have an additional adaptation that contributes to successful sexual reproduction. Glands near the testes produce fluid that nourishes sperm and helps them travel from the testes to the eggs of a female. Female Reproductive Organs Female animals have gonads called ovaries. Most female animals have two ovaries except female birds, which have only one ovary. Ovaries produce egg cells. Eggs are larger than sperm and cannot move on their own. Many female mammals are born with all the eggs they will ever have. You will read more about the testes and ovaries of humans in Chapter 13. How does animal fertilization occur? As you read earlier in this chapter, sexual reproduction requires fertilization—the fusion of a haploid egg cell and a haploid sperm cell that forms a diploid zygote. The way in which a sperm reaches the egg differs among animal species.

144 Chapter 3 • Reproduction of Organisms Internal Fertilization When fertilization happens inside the body of an organism, it is called internal fertilization. For many animals, the male has a specialized structure that can deposit sperm in or near a female’s reproductive system. The sperm swim to the egg or eggs. Earth- worms, spiders, insects, reptiles, birds, and mammals have internal fertilization. Internal fertilization ensures that an embryo, which develops from a fertilized egg, is protected and nourished until it leaves the female’s body. This protection increases the chance that the embryo will survive, develop into an adult, and reproduce. External Fertilization A female toad, like the one shown in Figure 17, deposits unfertilized eggs under water. A male toad releases his sperm above the eggs as she lays them. Fertilization that occurs in the environment, outside of an animal’s body, is called external fertilization. In most cases, the female animal releases eggs into water at about the same time a nearby male animal releases sperm into the water. When a sperm reaches an egg, fertilization takes place. Animals that reproduce using external fertilization include jellyfishes, clams, sea urchins, sea stars, many species of fish, and amphibians. Most animals that reproduce using external fertilization do not care for the fertilized eggs or for the newly hatched young. As a result, eggs and young are exposed to predators and other dangers in the environment, reducing their chances of surviving. Success- ful reproduction of animals with external fertilization requires that a large numbers of eggs be produced. This helps to ensure that at least a few offspring will survive to become adults that reproduce. For example, a female California red abalone, a species of sea snail, produces about 2.5 million eggs in one breeding season.

Figure 17 For organisms that have external fertilization, mating behaviors, such as that of the toads shown here, help make certain that eggs are fertilized as soon as possible after they leave the body of the female. Infer why a female toad releases large numbers of eggs into the water.

Lesson 3 • Animal Reproduction 145 Figure 18 In most mammals, 9jX`"W^aaZY the embryo develops inside the eaVinejhZ\\ body of the mother. The duck- billed platypus is an exception. Each duck-billed platypus embryo develops inside an egg laid in a nest. It hatches and is cared for by the mother. Compare How does the size of a duck- billed platypus egg compare with the size of a chicken egg?

How do animal embryos develop? The zygote produced by fertilization is only the beginning of an animal’s life. The zygote grows by mitosis and cell divisions and becomes an embryo—the next stage in an animal’s life. A growing embryo needs nourishment and protection from predators and other dangers in the environment. Different animals have different ways of supplying the needs of an embryo. In some animals, the embryo develops outside the body of the mother. In others, the embryo develops inside the mother. External Development The duck-billed platypus, as shown in Figure 18, is an example of an animal whose embryos develop outside the mother. Animals that develop outside the mother usually are protected inside an egg. In most instances, one embryo develops inside each egg. Most eggs contain a yolk that provides food for the developing embryo. Some kind of covering surrounds the egg. The covering protects the embryo, helps keep it moist, and discourages predators. Eggs laid by lizards, snakes, and other reptiles have a tough, leathery covering. A tough, jellylike substance usually surrounds eggs laid under water. As shown in Figure 19, bird eggs, like those of a robin, have a hard covering called a shell.

Figure 19 A female robin usually lays four eggs in a nest. Each egg Nda` contains an embryo and a yolk that supplies food for the growing embryo.

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Metamorphosis Some animals—including amphibians and many animals without backbones—go through more than one phase of development. Metamorphosis is a developmental process in which the form of the body changes as an animal grows from the egg to an adult. WORD ORIGIN metamorphosis The metamorphosis of a ladybug beetle and the metamorphosis from meta- (Greek, means of a frog are shown in Figure 20. A ladybug beetle goes through change) and morphe (Greek, four stages during its development—egg, larva, pupa, and adult. means form) The tadpole is the larval stage of a frog. Larva and adult forms often have different lifestyles. The larva of the frog lives only in the water. The adult frog can live on land or water. What developmental process does a tadpole go through as it becomes a frog?

Lesson 3 • Animal Reproduction 147 Internal Development The embryos of some animals, including most mammals, develop inside the mother. These embryos get nourishment from the How fast do they grow? mother. An organ or tissue transfers nourish- A human fetus develops for nine months ment from the mother to the embryo. Other inside its mother. Most human babies embryos, such as those of some snakes, insects, weigh less than ten pounds at birth. How and fishes, develop in an egg with a yolk while fast does a baby grow before it’s born? it is inside the mother. For these animals, the Data yolk, not the mother, provides nourishment for Examine the table below. It shows data the developing young. The young hatch from about how the mass of a human fetus the eggs while they are inside the mother and increases as it grows inside its mother. then leave the mother’s body. Where does an embryo that Increase in Mass of develops in an egg inside the a Human Fetus mother get its nourishment? Age of Fetus Mass of Fetus Gestation 16 weeks 180 g The length of time between fertilization and birth of an animal is called gestation. Gesta- 20 weeks 300 g tion varies from species to species and usually 24 weeks 680 g relates to the size of the animal at birth—the smaller the animal, the shorter its gestation. 28 weeks 1,135 g For example, gestation for a mouse is about 21 days; a dog, about 60 days; humans, about 32 weeks 1,680 g 266 days; and an elephant, about 600 days. A 36 weeks 2,500 g kangaroo is an exception. Gestation for a kangaroo is 35 days. A kangaroo is only about 40 weeks 3,360 g 2.5 cm long at birth, as shown in Figure 21.

Source: http://www.dcdoctor.com/pages/rightpages_ wellnesscenter/pregnancy/fetaldevelopment.html Figure 21 A newborn kangaroo crawls Data Analysis into a pouch on the mother’s body. It feeds and grows inside the pouch until it is large 1. Graph the growth of the fetus. enough to live on its own. 2. Describe your graph. Did the fetus grow the same rate for each four-week period? 3. Estimate the mass of the fetus at 8 weeks, at 18 weeks, and at 38 weeks. 4. Evaluate Could you estimate other points on the graph by looking at the graph line? Explain why or why not.

2.a, 7.c

148 Chapter 3 • Reproduction of Organisms Animal Reproduction Summary In this lesson, you learned how animals reproduce sexually. Males produce sperm in organs called testes. Females produce eggs in organs called ovaries. Internal fertilization takes place inside the female’s reproductive system. External fertilization takes place outside the female, in the environment. Embryos that develop inside the body of the female are nourished and protected until they leave the female’s body at birth. Embryos that develop outside the body of the female most often develop inside an egg. An egg has a protective covering and a yolk that provides nourishment to the developing embryo.

LESSON 3 Review

Summarize Standards Check Create your own lesson Using Vocabulary 4. What are the haploid cells that form in female animals? 2.b summary as you design a 1. Distinguish between testes and visual aid. ovaries. 2.a A. testes C. eggs 1. Write the lesson title, B. ovaries D. sperm number, and page num- 2. In your own words, write the bers at the top of your definition for metamorphosis. Applying Science 2.a poster. 5. Hypothesize why snake eggs 2. Scan the lesson to find Understanding Main Ideas have leathery shells. 2.a the red main headings. 6. Predict whether an animal Organize these headings Use the image below to answer that reproduces by external on your poster, leaving question 3. space between each. fertilization is more likely to IZhiZh live in water or on land. 3. Design an information Explain your reasoning. 2.a box beneath each red heading. In the box, list 7. Organize Information Copy 2–3 details, key terms, the graphic organizer below and definitions from each and list types of animal blue subheading. development mentioned in 4. Illustrate your poster with this lesson. 2.a diagrams of important structures or processes next to each information 3. How would you describe the box. organ system above? A. asexual C. female 2.a ELA7: W 2.5 B. embryo D. male Science nline For more practice, visit Standards Check at ca7.msscience.com.

Lesson 3 • Animal Reproduction 149 Life Span Conversions 2.a Life spans vary greatly among species of insects. Insect life spans are sometimes given in days, weeks, months, and years. In order to make MA7: NS 1.0, MG 1.1 a comparison of life spans among insects, the average life spans must be in the same unit.

Example Insect Life Spans How many times longer does the green lacewing Species Average Life Span live than the housefly? Housefly 1 week What you know: Green lacewing 30 days • Life span of the green lacewing: 30 days Mountain pine beetle 1 year • Life span of the housefly: 1 week Angular-winged 360 days What you need to find: katydid • How many times longer does the green Australian walking 8 months lacewing live than the housefly? stick 1 First convert both life spans to the same unit. Common earwig 355 days • The green lacewing life span is measured Darkling beetle 11 years in days. The housefly life span is measured Honey bee queen 4 years in weeks. Honey bee drone 5 weeks • Choose to convert the larger unit, weeks, into the smaller unit, days. Now find how Madagascar hissing 2 years (in captivity) many days are in 1 week. There are 7 days in cockroach 1 week. Oregon silverspot 3 months 2 Now you have both insect life spans butterfly measured in the same units to compare. The Vietnamese walking 6 months green lacewing life span is 30 days, and the house- stick fly life span is 7 days. To find how many times greater the green lacewing life span is than the housefly life span, divide 30 by 7. .is about 4.3 7 ، 30 Answer: The green lacewing lives about 4.3 times longer than the housefly.

Practice Problems 1. How many times longer does the honey bee queen live than Science nline the honey bee drone? For more math practice, visit Math Practice at 2. How many times longer does the Australian walking stick live ca7.msscience.com. than the Vietnamese walking stick?

150 Chapter 3 • Reproduction of Organisms LESSON 4

Science Content Asexual Reproduction Standards 2.a Students know the differences >Ê`i> Asexual reproduction produces offspring that are between the life cycles and reproduction identical to the parent. methods of sexual and asexual organisms. Real-World Reading Connection Have you ever joked about Also covers: 7.a, 7.c, 7.d, 7.e wanting to clone yourself? That way, you could enjoy time with your friends while your clone does chores and homework. Do Reading Guide any organisms reproduce by making exact copies of themselves? > } What You’ll Learn W`ihat> *isVÌÕ Àasexuali reproduction?

▼ Define asexual When,i>` we} think of reproduction, we usually think of reproduction. sexual reproduction.iV Recall that sexual reproduction occurs when a sperm and egg fuse, and it usually requires two

▼ Differentiate between regeneration and cloning. parents. However, many organisms have only one parent. Asexual reproduction is the production of offspring by one

▼ Compare an asexually produced offspring to its parent without a sperm and an egg joining. Asexual reproduc- parent. tion results in offspring that are genetically identical to the parent organism. The poinsettias shown in Figure 22 were pro- Why It’s Important duced by asexual reproduction. Learning about asexual reproduction will help you Advantages of Asexual Reproduction understand how cloning and Unlike sexual reproduction, asexual reproduction does not other techniques determine require a mate. Therefore, an asexually reproducing organism genetic traits of organisms. does not have to spend time and energy finding a mate. Also, to reproduce a number of offspring asexually takes less time than Vocabulary to reproduce the same number of offspring sexually. Since par- asexual reproduction ent and offspring are genetically identical, both are equally well fission budding adapted to the same environmental conditions. regeneration cloning Figure 22 Asexual reproduction makes it possible for a Review Vocabulary grower to produce hundreds of genetically identical poinsettias for the holiday season. prokaryote: organism made of a cell that does not have a membrane-bound nucleus (p. 64)

Lesson 4 • Asexual Reproduction 151 Disadvantages of Asexual Reproduction The major disadvantage of asexual reproduction is the lack of genetic variation. Recall that genetic variation in a population increases the chances that a few individuals will survive a change in the environment. Imagine a population of poinsettia plants growing in a greenhouse, like those shown in Figure 22. Suppose a greenhouse worker unknowingly plants the poinsettias in soil con- taminated with disease-causing bacteria. Because the poinsettias are genetically identical, the disease might affect all of them. The entire poinsettia population might be destroyed. Another disadvantage of asexual reproduction involves genetic changes, or mutations, that can occur. A harmful mutation in cells of an organism will be passed to asexually reproduced offspring. This could affect the offspring’s ability to survive.

What are two disadvantages of asexual reproduction?

What are the types of asexual reproduction? There are many types of asexual reproduction. However, each type involves cell division. Prokaryotes, or bacteria, reproduce WORD ORIGIN asexually by cell division that does not involve mitosis. Eukaryotes fission from Latin fissionem; means a reproduce asexually by mitosis and cell division. breaking up, cleaving Fission A bacterium has a small, circular DNA chromosome but no Figure 23 During fission, nucleus. Bacteria reproduce asexually by a process called fission, a bacterium grows while its DNA is replicated. When as shown in Figure 23. Fission produces two genetically identical the DNA has replicated and cells. Asexual reproduction by fission can occur rapidly. E. coli, a the cell is about twice its species of bacteria found in human intestines, can reproduce asex- original size, the two DNA ually every twenty minutes. copies separate. The cell membrane grows inward and the cell divides in half to produce two identical 8 daughter cells.

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152 Chapter 3 • Reproduction of Organisms Figure 24 Diatoms belong to a group of single-celled, How eukaryotic organisms called protists. They live in water and do yeast make their own food through reproduce? photosynthesis. What happens when you add sugar and warm water to dried yeast?

Mitotic Cell Division Some single-celled eukaryotes, such as the diatom in Figure 24, reproduce asexually by mitotic cell division—mitosis followed by cell division. Recall from Chapter 2 that mitosis and cell division Procedure produce two genetically identical cells from one cell. Asexual reproduction in a single-celled eukaryote also produces two identical cells, except that each cell is an individual organism. 1. Complete a lab safety form. Budding 2. Pour 125 mL of 34°C Yeasts are single-celled eukaryotes that are related to mush- water into a cup or beaker. rooms and other fungi. As shown in Figure 25, yeast cells repro- 3. Add 5 g of sugar and duce by budding—a type of asexual reproduction in which a new 5 g of yeast to the organism forms on the parent organism. The new organism is water. Stir slightly. called a bud and forms by mitosis and cell division. It is genetically Record your observa- identical to the parent and eventually separates from the parent to tions after 5 min. live on its own. 4. Using an eyedropper, put a drop of yeast Some multicellular animals, such as freshwater hydra also solution on a micro- shown in Figure 25, can reproduce by budding. Notice how the scope slide. Place a bud grows from the stalk of the parent hydra. Like many multi- coverslip over the cellular eukaryotes, including plants, hydras can reproduce both drop. sexually and asexually. 5. View the yeast solution under a microscope. Draw what you see. Figure 25 This yeast cell is budding. Analysis The bud of the hydra looks like a smaller 1. Describe evidence of version of the parent. yeast reproduction. Compare the genetic makeup of the hydra 2. Identify the process bud to the hydra parent. you observed under the microscope. Bud Bud 2.a, 7.a, 7.c, 7.d

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Lesson 4 • Asexual Reproduction 153 ! " #$# %&$##'#( Figure 26 New, genetically identical plants grow from the horizontal stems, or runners, of strawberry plants. A kalanchoe plant forms so many plantlets that it is known as the maternity plant.

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ACADEMIC VOCABULARY Plant Cuttings differentiate (dih fuh In Lesson 3, you read how plants reproduce sexually. Many REN chee ayt) plants can also reproduce asexually. If you cut a green stem from a (verb) to show a difference between two or more things. houseplant and place it in water, roots and leaves can grow, pro- Students must be able to differ- ducing a new plant. A new plant grown from a stem cutting is entiate meiosis from mitosis. genetically identical to the parent plant. Poinsettias, like those in Figure 22, can be grown from stem cuttings. Depending on the type of plant, leaf cuttings or root cuttings can also be used to grow a new plant. Figure 27 Sea stars Some plants propagate themselves asexually. The kalanchoe can reproduce asexually plant shown in Figure 26 has produced tiny plantlets at the edges by regeneration. of its leaves. These plantlets can fall to the ground, take root, and Identify the kind of cell division that takes place when produce new plants. A strawberry plant, as shown in Figure 26, a sea star regrows missing produces new plants along horizontal stems that grow on the sur- body parts. face of the ground. Animal Regeneration Recall from Chapter 2 that the process in which cells in an embryo become different types of cells is called cell differentiation. But as you just read, some plant cells can dedifferentiate—change from a differentiated cell type and grow into other cell types. You also read in Chapter 2 that differentiated human cells cannot change and grow into other cell types. However, some animals have cells that can change into other cell types.

Producing New Animals Asexual reproduction that produces new animals from pieces of an animal’s body is called regeneration. The sea star shown in Figure 27 can asexually reproduce by regeneration. If it is broken into pieces, each piece can grow the missing parts. The new organisms are genetically identical.

154 Chapter 3 • Reproduction of Organisms Producing Body Parts Sometimes, the term regeneration is used WORD ORIGIN to describe growth that replaces a missing part of an animal. For regeneration example, if a sea star just loses part of an arm, it can regrow that from Latin regeneratus; means make over lost part. The regrowth of a body part is not an example of asexual reproduction, because a new individual is not created. What is cloning? Fission, budding, and regeneration are all types of asexual reproduction that produce genetically identical offspring in nature. In the past, the term cloning described any process that produced genetically identical offspring. Today, however, cloning usually refers to a method of asexual reproduction developed by scientists and performed in laboratories. Cloning produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism.

Give two different meanings for cloning.

Plant Cloning Plant tissue culture is a cloning technique that enables scientists to produce genetically identical plants from a few plant cells grown in a test tube, as shown in Figure 28. Plant tissue culture can be used to produce thousands of identical plants from a plant that has desirable genetic traits, such as high nutritional value or rapid growth.

Figure 28 New carrot plants can be produced from cells of a carrot root using tissue culture techniques.

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The first animal to be successfully cloned from an adult cell was a sheep. In 1996, scientists in Scotland cloned a female sheep that they named Dolly. Figure 29 illustrates the reproductive methods used to make Dolly. Since then, scientists have cloned other animals, including mice, cows, and a horse. Although several cloned animals have been produced successfully, they often are not as healthy as animals produced by sexual reproduction. Some animal clones, including Dolly, have had a much shorter life span than animals produced by sexual reproduction. Animal cloning raises ethical issues that people are con- cerned about. For example, many people think the cloning of humans should never be allowed. You might be asked to consider issues like this during your lifetime.

Figure 29 Scientists used three different sheep to produce the cloned sheep known as Dolly. H]ZZeM H]ZZeN Infer how the genetic makeup of Dolly compares to the genetic makeup of sheep Y.

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9daan 8adcZd[h]ZZeM Dolly Sheep Z Asexual Reproduction Summary In this lesson, you read that many organisms reproduce asexually, which means they have only one parent. Offspring from asexual reproduction have genetic material that is identical to the genetic material of the parent. Bacteria reproduce asexually by fission, which is a type of cell division. Some eukaryotes, including yeast, reproduce asexually by budding. Other eukaryotes reproduce asexually by mitosis and cell division. Parts of plants, such as stem cuttings or root cuttings, can grow into new plants. In some animals, a body part can regenerate and form a new individual. Cloning is a scientific process that produces offspring genetically identical to one parent organism.

LESSON 4 Review

Summarize Standards Check Create your own lesson Using Vocabulary 6. Distinguish between fission and budding. 2.b summary as you design a Match these terms with the correct study web. definition. Applying Science 1. Write the lesson title, number, and page num- cloning 7. Debate how the use of animal bers at the top of a sheet regeneration cloning might affect the food of paper. 1. the growth of a new individual industry. 2.b 2. Scan the lesson to find from a broken-off portion of 8. Organize Information Draw the red main headings. another animal’s body 2.b a graphic organizer similar to 3. Organize these headings 2. a method of asexual reproduc- the one below to list the types clockwise on branches tion developed by scientists of asexual reproduction. Write around the lesson title. and performed in laboratories Asexual Reproduction in the 4. Review the information 2.b center oval. 2.b under each red heading to design a branch for Understanding Main Ideas each blue subheading. 3. Which term does not apply to 5. List 2–3 details, key terms, asexual reproduction? and definitions from each blue subheading on A. budding C. cloning 2.b branches extending B. fission D. fertilization

from the main heading 4. How do prokaryotes reproduce? branches. A. budding C. fission 2.b ELA7: W 2.5 B. cloning D. regeneration 5. Discuss advantages and disadvantages of asexual Science nline reproduction. 2.b For more practice, visit Standards Check at ca7.msscience.com .

Lesson 4 • Asexual Reproduction 157 Plant Propagation Problem Materials You know that plants can reproduce both sexually and asexually. coleus seeds Coleus plants are easy to reproduce both ways: from seeds and coleus plants from stem cuttings. In this lab, you will get a chance to try both packaged potting soil methods. containers clear plastic wrap Form a Hypothesis room-temperature Which method of propagating plants do you think will be the water most successful? Which one will grow faster? Which one will have a lower rate of failure? Write two hypotheses. Collect Data and Make Observations 1. Read and complete a lab safety form before you begin. 2. Design and construct a data table to record your daily observations and the measured height of the seedlings Safety Precautions and cuttings. Part A 3. Obtain three seeds from your teacher. Science Content 4. Plant the seeds in a container of damp potting soil, as Standards directed by your teacher. 2.a Students know the differences 5. Loosely cover the top of the container with a piece of clear between the life cycles and reproduction plastic wrap. Place the containers in a bright location, away methods of sexual and asexual organisms. from cold or hot drafts of air and away from direct sun. 7.a Select and use appropriate tools and 6. Each day, remove the plastic wrap so that you can sprinkle technology (including calculators, computers, balances, spring scales, the top of soil with room-temperature water, and then microscopes, and binoculars) to perform replace the plastic wrap. tests, collect data, and display data. 7. Every other day, measure the height of the seedlings and 7.c Communicate the logical connection record this data and other observations in your data table. among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence. 7.e Communicate the steps and results from an investigation in written reports and oral presentations.

158 Part B

8. Cut a stem of the plant just below the third set of leaves, as shown in the photo to the right. 9. Remove the bottom set of leaves. 10. Place the cutting into a container of damp potting soil. The spot on the stem where the leaves were attached must be below the soil’s surface. 11. Repeat steps 1–3 twice. 12. Sprinkle the top of the soil daily with room-temperature water. 13. Every other day, measure the height of the cuttings and record this data and other observations in your data table. Analyze and Conclude 1. Identify which trial was sexual reproduction and which one was asexual. 2. Describe the growth of the seedlings and cuttings. 3. Graph the average growth of the three seedlings over the observation period. 4. Graph the average growth of the three cuttings over the observation period. 5. Evaluate your hypotheses. Were they correct? Explain why or why not. How would you adjust your hypotheses if you were going to do another experiment? 6. Error Analysis Which of your trials worked better? Use scientific explanations to explain your results. Communicate 3CIENCE Take your plants from this experiment and plant them in a public garden, near a retirement home, or in an outdoor space that needs cheering up. Remember to water them regularly. Putting some bark or leaf mulch around your plants will help keep them moist. Create a sign that explains how the plants were produced. With permission, post your sign near your plants.

159 Lions and Tigers and Bears, Oh My! Animals can have infections, sprain joints, or need medicines and vaccines. Instead of a physician, a veterinarian cares for animals. Veterinarians often help female animals with the delivery of their young. Some veterinarians take care of small domestic animals, like cats or dogs, but large animals need care too. Large- animal vets spend time caring for farm animals, like horses and cows, or zoos animals, such as lions, tigers, and bears. Work in pairs. Pretend you’re a news reporter interviewing a large-animal veterinarian. Ask about his or her day on the job, including the kinds of problems he or she encountered, and how he or she fixed them.

Producing Disease-Free Plants Plant tissue culture is used to produce disease-free plants. When a virus enters a plant, it usually infects the entire plant. However, scientists have learned that the rapidly reproducing cells at the tips of stems remain disease-free in a virus-infected plant. Using tissue culture techniques, scientists can reproduce virus-infected plants without transferring the virus to the new plants.

Visit TTechnologyechnology at ca7.msscience.com to research plant tissue culture. Write a paragraph about how tissue culture technology helps farmers and other plant growers. ELA7: W 1.2

160 (t)Paddy Ryan/Animals Animals, (b)Jim Richardson/CORBIS Ernest Everett Just and Parthenogenesis Ernest Everett Just was an African-American scientist who became well-known for his research into cell fertilization and embryology at the beginning of the twentieth century. Just was interested in learning about the structure of healthy cells as a means of curing disease. He also studied parthenogenesis (par thuh noh JEH nuh sus)—how some embryos can develop without fertilization. How can an organism develop from an unfertilized egg? Visit HHistoryistory at ca7.msscience.com to research parthenogenesis. Compile a class list of organisms that undergo parthenogenesis.

Animal Cloning—Yes or No? Since 1996, several types of mammals have been cloned using the process that created Dolly, the sheep. The process uses genetic material from adult cells, which allows animal breeders to create clones that have traits observed in the adult animal. These calves—Dot and Ditto—are clones of an adult cow. Animal cloning is controversial. Write an editorial for or against animal cloning. Use scientific evidence to support your position. ELA7: W 2.4

161 SPL/Photo Researchers CHAPTER Standards Study Guide

Different types of reproduction ensure the survival of different species. / iÊ Ê`i>

Lesson 1 Sexual Reproduction and Meiosis 2.b, 7.b >Êì> Meiosis maintains the chromosome • diploid (p. 129) number of a species from one generation to the • egg (p. 126) next. • fertilization (p. 126) • haploid (p. 129) • Sexual reproduction includes the fusion of a sperm cell with an egg cell to produce a new organism. • meiosis (p. 128) • sexual reproduction (p. 126) • Meiosis is cell division that produces sperm and egg cells. > } • sperm (p. 126) • Meiosis>ì> maintains } *a constantVÌÕÀi number of chromosomes from • zygote (p. 126) ònei> generation*VÌÕÀi of sexually produced offspring to the next. Lesson,i>`} 2 Plant Reproduction 2.a, 5.f, 7.b i,Vi>`} >Êì> Ai plant’sV life cycle includes a diploid • angiosperm (p. 138) • pollen grain (p. 136) generation that produces spores and a haploid • anther (p. 138) • pollen tube (p. 139) generation that produces eggs and sperm. • embryo (p. 137) • pollination (p. 137) • filament (p. 138) • seed (p. 137) • The life cycle of all plants includes an alternation of generations. • fruit (p. 139) • spore (p. 135) • ovary (p. 138) • stamen (p. 138) • Angiosperms are flowering plants that produce seeds • ovule (p. 137) • stigma (p. 138) enclosed in a fruit. > } • pistil (p. 138) • style (p. 138) ì> *VÌÕÀi Lesson 3 Animal Reproduction 2.a, 2.b, 7.c ,i>`} iV >Êì> Animals have specialized structures for • gonad (p. 144) sexual reproduction. • metamorphosis (p. 147) • ovary (p. 144) • Animals have specialized organs, called gonads, for sexual reproduction. • testes (p. 144) • In some animal species, fertilization happens outside the body; in other species, fertilization happens inside the body. • In> some animal } species, embryos develop outside the `mother;i> in* VotherÌÕÀi species, embryos develop inside the mother. ,i>`} 2.a, 7.a, 7.c, 7.d, 7.e Lesson iV 4 Asexual Reproduction >Êì> Asexual reproduction produces off- • asexual reproduction (p. 151) spring that are identical to the parent. • budding (p. 153) • cloning (p. 155) • Asexual reproduction requires only one parent. • fission (p. 152) • Types of asexual reproduction include fission, budding, • regeneration (p. 154) mitosis, and cloning. Download quizzes, key terms, and flash cards from > } ca7.msscience.com. ì> *VÌÕÀi

,i>`} 162 Chapter iV 3 • Standards Study Guide Interactive Tutor ca7.msscience.com Standards Review CHAPTER

Linking Vocabulary and Main Ideas Use vocabulary terms from page 162 to complete this concept map.

Sexual Reproduction

requires requires

1. 2.

which produces which is the fusion of

3. and 4.

which combine to form a

Visit ca7.msscience.com for: Using Vocabulary ▶ Vocabulary PuzzleMaker ▶ Vocabulary eFlashcards Write the vocabulary term that best matches each phrase. ▶ Multilingual Glossary 6. process that produces haploid cells from a diploid cell 7. process that produces a diploid cell from two haploid cells 8. cells that have two of each chromosome 9. generation of a plant that produces eggs and sperm 10. part of the flower that will become a fruit 11. produces sperm 12. asexual reproduction used by prokaryotes 13. produces a new individual from a part of an animal or plant 14. method scientists use to make identical offspring from adult cells

Chapter 3 • Standards Review 163 CHAPTER Standards Review

Understanding Main Ideas 6. Which term describes the development of a Use the image below to answer question 1. tadpole into an adult frog? A. alternation of generations 2.b B. fertilization C. meiosis D. metamorphosis

7. What method of asexual reproduction involves the regrowth of missing body parts from part of an organism? 1. What phase of meiosis is pictured above? A. budding 2.b A. anaphase I 2.a B. fission B. anaphase II C. cloning C. metaphase I D. regeneration D. metaphase II Use the image below to answer questions 8–10. 2. Which organism can reproduce asexually by &'() dedifferentiation of cells? A. diatom 2.b B. bacterium C. plant D. yeast

3. Which term describes the daughter cells produced by meiosis? A. identical 2.a B. diploid 8. What is the name of structure number 1? C. homologous A. anther 5.f D. haploid B. filament C. stigma 4. Which reproductive structure grows into the D. style haploid generation of a plant? A. cone 5.f 9. Where is pollen produced? B. seed A. 1 5.f C. sperm B. 2 D. spore C. 3 D. 4 5. What type of plant produces fruit? A. conifer 5.f 10. Which part of the flower becomes a seed? B. seedless A. 1 5.f C. gymnosperm B. 2 D. angiosperm C. 3 D. 4

164 Chapter 3 • Standards Review Standards Review ca7.msscience.com Standards Review CHAPTER

Applying Science 3CIENCE 2.a 11. Distinguish between mitosis and meiosis. 23. Write one paragraph describing the similarities Use the image below to answer question 12. and differences of sexual reproduction and asexual reproduction. ELA7: W 1.2

Applying Math

Use the table below to answer questions 24–27.

Insect Life Spans 12. Predict how many chromosomes each daughter cell of the cell above will have at the end 2.a Species Average Life Span of meiosis. Mountain pine beetle 1 year 13. Compare gymnosperms and angiosperms. 5.f Angular-winged katydid 360 days 14. Compare external fertilization and internal fertilization. 2.b Common earwig 355 days 15. Predict why most frog species enter water to Darkling beetle 11 years reproduce. 2.b 16. Suggest why animals that reproduce by external Madagascar hissing 2 years (in captivity) fertilization produce more eggs than animals cockroach that reproduce by internal fertilization. 2.b Oregon silverspot 3 months 17. Predict how the success of plants in a particular butterfly environment would be affected if the plants could not reproduce asexually. 2.b 24. How much longer does the darkling beetle 18. Hypothesize why bacteria are able to reproduce live than the mountain pine beetle? much more quickly than humans and other MA7: NS 1.0, MG 1.1 multicellular eukaryotic organisms. 2.b 25. How much longer does the Madagascar 19. Defend Some lizards can grow a new tail if hissing cockroach live than the angular- theirs breaks off. Is this asexual reproduction? winged katydid? MA7: NS 1.0, MG 1.1 Defend your answer. 2.b 20. Evaluate Yeasts are commonly used to make 26. How much longer does the common earwig bread. How might the bread-making process be live than the Oregon silverspot butterfly? affected if yeast could reproduce only sexually? MA7: NS 1.0, MG 1.1 2.b 21. Infer why seedless plants depend on water for 27. How much longer does the mountain pine beetle live than the Oregon silverspot fertilization, but seed plants do not. 2.a butterfly? MA7: NS 1.0, MG 1.1 22. Develop a concept map to identify if a plant is a gymnosperm, an angiosperm, or a seedless plant. 2.a

Chapter 3 • Standards Review 165 CHAPTER Standards Assessment

1 A new plant can grow from a white potato, as 4 Which describes what happens to chromosomes shown below. during meiosis? A Homologous chromosomes separate, then they replicate in meiosis II. B Replicated homologous chromosome pairs separate in meiosis I, then sister chromatids separate during meiosis II. C Sister chromosomes separate during meiosis I. D Homologous chromosomes stay together during meiosis I and meiosis II. 2.b

5 Bacteria reproduce by asexual reproduction, as shown below.

How does the genetic material of the new plant above compare to that of the potato? A identical B different C greater D less 2.a

2 Which term describes this type of What is the term used for this type of asexual reproduction? reproduction? A fission A fission B budding B budding C regeneration C regeneration D cloning 2.a D cloning 2.a

3 Which is the correct sequence for sexual 6 Which term means the joining of a sperm and reproduction? an egg? A sex cells, zygote, fertilization, meiosis A pollination B zygote, sex cells, meiosis, fertilization B mitosis C fertilization, meiosis, zygote, sex cells C fertilization D meiosis, sex cells, fertilization, zygote 2.a D meiosis 2.b

166 Chapter 3 • Standards Assessment Standards Assessment ca7.msscience.com Standards Assessment CHAPTER

Use the diagram below to answer questions 7 and 8. 10 Which is the correct sequence in the life cycle of a beetle? A A larva, adult, egg, pupa C B egg, larva, pupa, adult C pupa, egg, adult, larva D adult, pupa, larva, egg 2.a

Use the diagram below to answer questions 11 and 12. B

A 7 What does structure C represent? A stored food B embryo C ovary D seed covering 5.f

8 Which part(s) of this seed will grow into the D B new plant? C A A 11 Which letter represents the yolk? B C A A C A and C B B D C and B 5.f C C 9 What is the term used to describe the process of D D 2.a when a plant’s sperm-producing structure lands on the female reproductive structure of the same type of plant? 12 Which letter represents the developing organism? A pollination A A B mitosis B B C fertilization C C D meiosis 5.f D D 2.a

Chapter 3 • Standards Assessment 167